It is known to collect fluids in containers such a flexible bags. For example, it is known to collect blood and other physiological fluids during surgery by pumping the blood into flexible bags. The fluids are then redelivered to the patient after processing. The fluids generally include debris that must be removed, and filters are used for this. Prior bags that include filters have not been effective, however, and are often expensive. Moreover, because the bags are disposable, the fluid lines are detachable, and it is necessary to provide an effective means for ensuring that the lines are properly connected before the pumping operation begins.